This application is based upon and claims priority of Japanese Patent Applications No. 2001-040006, filed in Feb. 16, 2001 and Japanese Patent Applications No. 2001-332169, filed in Oct. 30, 2001, the contents being incorporated herein by reference.
1. Field of the Invention
The present invention relates to an optical deflecting element for deflecting the light, an optical switch module for switching a propagation destination of the light signal between a plurality of input ports and a plurality of output ports, a light signal switching device employing the optical switch module, and an optical wiring substrate having a mirror for changing the propagation direction of the light signal.
2. Description of the Prior Art
In recent years, the transmission band of the optical communication is increased steadily and also the higher speed and the larger capacity are accelerated conjointly with the progress of the WDM (wavelength division multiplexing) technology. In order to construct the hardware infrastructure of the optical fiber network in the trunk communication network, the light signal switching device f or switching the transmission destination of the optical signal is needed.
In th e prior art, the optical cross-connecting device that converts the light signal the electric signal once, then switches the transmission destination of the signal by the crossbar switch, and then converts the electric signal into the light signal once again is the mainstream as the light signal switching device. In this case, if the data transmission rate exceeds 10 Gb/s, it is difficult to construct the switching device by the electric switching elements like the prior art.
If the optical transmission path is switched by using the optical switching elements in place of the electric switching elements, the conversion between the light and the electricity is not needed and thus the optical cross-connecting device that does not depend on the rate (frequency) of the light signal can be constructed. At present, the optical switch module whose input port number is 32 and whose output port number is 32 (32xc3x9732 channels) is implemented. Also, there is the example in which the nonocclude switching network (light signal switching device) is constructed by connecting such optical switch modules in a multi-stage fashion.
In the optical switch module in the prior art, normally the movable micro mirror is employed as the optical switching element. That is, the propagation direction of the light signal is switched by controlling the direction of the micro mirror by the electric signal. The micro mirror can be formed by using the MEMS (MicroElectroMechanical System) technology. The optical switch module is constructed by arranging a number of micro mirrors in two directions (the X direction and the Y direction).
Also, the switching element (optical deflecting element) utilizing the electrooptic effect has been developed. FIG. 1A is a plan view showing the optical deflecting element in the prior art, and FIG. 1B is a sectional view showing the same (Patent Application Publication (KOKAI) Hei 9-5797). As shown in FIGS. 1A and 1B, in the optical deflecting element in the prior art, the optical waveguide 11 having the electrooptic effect is formed on the conductive or semi-conductive single crystal substrate 10, and then the upper electrode 12 is formed thereon. The upper electrode 12 is formed as a wedge shape (right triangle shape) having a side that orthogonally intersects with the optical axis of the incident light (called a base hereinafter) and a side that obliquely intersects with the optical axis (called an oblique side hereinafter).
In the optical deflecting element constructed in this manner, as shown in FIG. 1A, the light is incident upon the optical waveguide 11 from the base side of the upper electrode 12 and is emitted from the oblique side of the upper electrode 12. If the voltage is applied between the upper electrode 12 and the lower electrode while using the substrate 10 as the lower electrode, the refractive index of the optical waveguide 11 under the upper electrode 12 is changed to cause the difference in the refractive index of such portion among the periphery. The light passing through the optical waveguide 11 is refracted at the portion whose refractive index is changed and thus the traveling direction is changed. In other words, the outgoing direction of light can be controlled by changing the voltage that is applied between the upper electrode 12 and the substrate 10.
Meanwhile, in the case that the light signal is transmitted between the optical devices, it is possible to connect the optical devices via the optical fibers if the number of the wirings (optical wirings) is small. However, if the number of the wirings is in excess of several hundreds to several thousands, it is advantageous from respects of the easiness of the connecting operation and the space to connect the optical devices by the optical waveguides rather than the connection via the optical fibers.
It is rarely the case that all the optical waveguides for connecting the optical devices can be formed by the straight line. Normally, the optical waveguides are formed to detour the electric parts, the electric wirings, the connectors, and other optical waveguides mounted on the substrate. In this case, since the light has the high straight traveling property, the optical waveguides must be formed along the curve having the large curvature or the propagation direction of light must be changed sharply by the reflection mirror.
If the optical waveguides must be formed along the curve having the large curvature, the layout space of the optical waveguides is increased. Therefore, there is the drawback that it is difficult to form a large number of optical waveguides. In contrast, if the reflection mirror is employed, there is the advantage that the optical waveguides of high density can be integrated. As the reflection mirror, there are the total reflection mirror that totally reflects the light based on the difference in the refractive index and the metal mirror that is formed of the metal film.
The inventors of the present invention consider that problems described in the following are present in the above optical switch module in the prior art.
In the optical switch module that is constructed by integrating the micro mirrors, a module size of the 32xc3x9732 channel module containing light input/output ports (fiber connectors), for example, becomes several tens cm square. In order to achieve the nonocclude optical cross-connecting device on a scale of 1000xc3x971000 channels that is requested in the market, the optical switch modules must be constructed in a three-stage fashion by using 192 optical switch modules, for example.
Also, as described above, the wavelength division multiplexing (WDM) technology is employed to improve the throughput of the data transmission, and the light signal having plural wavelengths is transmitted collectively over one optical fiber. Therefore, the multiplied light signal must be passed through the optical branching filter to separate plural wavelengths into individual wavelengths before such multiplied light signal is input into the optical switch module. As the optical branching filter, there are the optical branching filter using the interference filter, the AWG (Arrayed Waveguide Grating) optical branching filter based on the waveguide technology, etc.
In addition, the optical multiplexer is needed to transmit the wavelength-multiplexed light signal once again after the propagation path of the light signal is switched by the light signal switching device. The optical multiplexer executes the multiplexing of the light signal based on the opposite principle to the optical branching filter.
Both the optical branching filter and the optical multiplexer are formed in the form of module and are connected to the optical switch module via the optical fiber. If the light signal switching device on the scale of 1000xc3x971000 channels is constructed by employing the conventional optical switch modules, the number of the optical fibers that connect the optical switch modules, the optical switch module and the optical branching filter, and the optical switch module and the optical multiplexer is increased up to 6000. For this reason, it is not practical to construct the light signal switching device on the scale of 1000xc3x971000 channels by the above optical switch modules in the prior art.
In Patent Application Publication (KOKAI) 2000-180905, there is set forth the optical switch (optical switch module) that has the incident side optical waveguide, the collimate lens, the optical deflecting element constructed by arranging the electrode on and under the slab waveguide, the converging lens, and the outgoing side optical waveguide. However, in the optical switch in Patent Application Publication (KOKAI) 2000-180905, the conductive or semi-conductive single crystal substrate is used as the common lower electrode to all the optical deflecting elements, and also all the upper electrodes are directed in the same direction. Therefore, the deflection angle of one optical deflecting element is small and thus the interval between the input side optical deflecting element and the output side optical deflecting element must be set large to increase the number of input/output ports. As a result, in the optical switch in Patent Application Publication (KOKAI) 2000-180905, the miniaturization of the device is insufficient.
The problems described in the following are considered in the optical deflecting element shown in FIGS. 1A and 1B.
In the optical deflecting element shown in FIGS. 1A and 1B, it is needed that the substrate 10 is conductive or semi-conductive. But it is not easy to form the conductive or semi-conductive single crystal substrate having the size required for the optical deflecting element, and thus the yield of fabrication is low.
Also, it is difficult to give the conductivity to the single crystal substrate to the same extent as the metal, the electric resistance of the substrate causes the signal delay, and the high-speed operation becomes difficult.
In addition, the electrode is provided on and under the substrate. Therefore, if the optical deflecting element is to be mounted on other substrate, one electrode can be connected directly to the substrate by the solder, or the like, but the other electrode must be connected individually to the electrode on the substrate via the wirings, or the like. As a result, there is such a drawback that the packaging steps become complicated.
The problems described in the following are considered in the optical wiring substrate having the reflection mirror in the prior art.
That is, as described above, as the reflection mirror employed in the optical wiring, there are the total reflection mirror and the metal mirror. The metal mirror can avoid the transmission of light substantially perfectly if the type and the film thickness of the metal are set properly. In this case, since a part of light is absorbed by the metal film, it is impossible to suppress the optical loss to zero. Also, in the optical wiring circuit, in some cases the reflection mirror must be formed perpendicularly to the substrate surface. But there is also the problem that it is difficult to form the metal film on the surface that is perpendicular to the substrate surface.
The total reflection mirror utilizes the event that, when the light goes into the interface between the layer of the high refractive index and the layer of the low refractive index at an angle that is larger than the critical angle, such light can be totally reflected. However, since the light propagates through the optical waveguide to have a certain angular width, a part of the light does not satisfy the total reflection condition and then transmits through the total reflection mirror to cause the optical loss.
It is an object of the present invention to provide an optical switch module a size of which can be reduced much more in contrast to the prior art, and a light signal switching device constructed by employing the optical switch module.
It is another object of the present invention to provide an optical deflecting element which can execute the high-speed operation without the conductive or semi-conductive substrate and which can be mounted on other substrate by simple steps, and an optical switch module constructed by employing the optical deflecting element.
It is still another object of the present invention to provide an optical wiring substrate having a mirror which has small loss and which is readily manufactured.
An optical switch module set forth in claim 1 of the present invention comprises a collimate portion for collimating individually a plurality of light signals respectively; a plurality of first optical deflecting elements for switching propagation directions of the light signals, which are passed through the collimate portion, individually respectively by utilizing an electrooptic effect; a common optical waveguide through which the light signals, which are passed through the plurality of first optical deflecting elements respectively, are propagated; a plurality of second optical deflecting elements for switching the propagation directions of the light signals, which are passed through the common optical waveguide, individually respectively by utilizing the electrooptic effect; and a converging portion for converging the light signals, which are passed through the plurality of second optical deflecting elements, individually respectively; wherein each of the first optical deflecting elements and the second optical deflecting elements is constructed by one or plural prism pairs, and each of the prism pairs includes a slab waveguide formed of material having the electrooptic effect, first and second upper electrodes formed as a wedge shape and arranged on a light signal passing area of the slab waveguide such that wedge top ends are directed mutually oppositely, and first and second lower electrodes arranged under the slab waveguide so as to oppose to the first and second upper electrodes.
In the present invention, the prism pair is employed as an optical deflecting element. The prism pair is constructed by the slab waveguide formed of material having the electrooptic effect, and first and second upper electrodes and first and second lower electrodes arranged on and under the slab waveguide. These electrodes are shaped into the wedge shape (e.g., a triangular shape), and change the refractive index of a part of the slab waveguide by utilizing the electrooptic effect to change the propagation direction of light. In this case, since the propagation direction of light is changed between the first upper electrodes and the first lower electrodes and also the propagation direction of light is changed between the second upper electrodes and the second lower electrodes, the propagation direction of light can be largely changed. Also, since the first and second upper electrodes are arranged such that their wedge top ends are directed mutually oppositely, the first lower electrodes are opposed to the first upper electrodes, and the second lower electrodes are opposed to the second upper electrodes, the alignment density of the electrodes can be increased. Because of these reasons, the size of the optical switch module can be extremely reduced rather than the prior art.
Also, since the prism pairs, the collimate lens, the converging lens, etc. are formed integrally on the substrate, the size of the optical switch module can be reduced much more.
A light signal switching device set forth in claim 5 of the present invention comprises a first optical switch module group constructed by arranging a plurality of first optical switch modules; a second optical switch module group constructed by arranging a plurality of second optical switch modules and connected optically to the first optical switch module group; and a third optical switch module group constructed by arranging a plurality of third optical switch modules and connected optically to the second optical switch module group; wherein each of the first, second and third optical switch module includes (1) a collimate portion for collimating individually a plurality of light signals respectively, (2) a plurality of first optical deflecting elements for switching propagation directions of the light signals, which are passed through the collimate portion, individually respectively by utilizing an electrooptic effect, (3) a common optical waveguide through which the light signals, which are passed through the plurality of first optical deflecting elements respectively, are propagated, (4) a plurality of second optical deflecting elements for switching the propagation directions of the light signals, which are passed through the common optical waveguide, individually respectively by utilizing the electrooptic effect, and (5) a converging portion for converging the light signals, which are passed through the plurality of second optical deflecting elements, individually respectively, and wherein each of the first and second optical deflecting elements is constructed by one or plural prism pairs, and each of the prism pairs includes a slab waveguide formed of material having the electrooptic effect, first and second upper electrodes formed as a wedge shape and arranged on a light signal passing area of the slab waveguide such that wedge top ends are directed mutually oppositely, and first and second lower electrodes arranged under the slab waveguide so as to oppose to the first and second upper electrodes.
Since the light signal switching device of the present invention employs the optical switch module having the above structure, the optical switch modules, the optical branching filter and the first optical switch module group, and the third optical switch module group and the optical multiplexer is connected via optical connectors having a plurality of lenses, which are aligned in a one-dimensional or two-dimensional direction, for example, respectively. Accordingly, the size of the device can be extremely reduced rather than the conventional light signal switching device in which respective devices are connected via the optical fibers.
An optical wiring substrate set forth in claim 13 of the present invention comprises an optical waveguide having a bended shape; and a dielectric multi-layered film mirror having a plurality of slits provided to a bending portion of the optical waveguide as a part of a multi-layered structure.
The lights are multiply-reflected by respective layers of the dielectric multi-layered film mirror, but the lights cause the loss if these lights cannot enter into the inside of the optical waveguide. Therefore, in order to guide the light reflected in the interior of the multi-layered structure so as to enter into the optical waveguide, the plane that is parallel with the reflection plane of the dielectric multi-layered film mirror and contains an intersection point of center lines of the optical waveguide at the bending portion is set in the inside of the dielectric multi-layered film mirror.
As normally known, if the material, the thickness of respective layers, and the layer number of the high refractive-index layer and the low refractive-index layer are set properly in response to the wavelength of the reflected light, the dielectric multi-layered film mirror can get the reflectance of 100%. Since the lights propagate through the optical waveguide with a certain angle width, a part of the lights does not satisfy the total reflection conditions. Mainly such light out of the lights, that are incident upon the reflection plane of the dielectric multi-layered film mirror, has the small angle to the normal of the reflection plane. Therefore, if a periodic structure of dielectric layers of the dielectric multi-layered film mirror is set to lights, that have a smaller angle to a normal of a reflection plane than a center line of the optical waveguide, out of lights that are incident upon the reflection plane, the lights that transmit through the dielectric multi-layered film mirror can be returned into the inside of the optical waveguide. As a result, the loss caused by the dielectric multi-layered film mirror can be further reduced rather than the prior art.
An optical deflecting element set forth in claim 21 of the present invention comprises a substrate; a first electrode formed on the substrate; an optical waveguide formed on the first electrode and having an electrooptic effect; a wedge-shaped second electrode formed on the optical waveguide at a position that opposes to the first electrode; and a leading electrode formed on the optical waveguide and connected electrically to the first electrode.
In the optical deflecting element of the present invention, since the first electrode is formed on the substrate, the substrate that is suitable for the formation of the optical waveguide can be employed irrespective of the presence of the conductivity of the substrate. Also, in the optical deflecting element of the present invention, the second electrode and the leading electrode are formed on the identical plane, and the lights can be deflected by applying the voltage between these electrodes. Therefore, when the optical deflecting element is mounted on other substrate, these electrodes can be jointed simultaneously to other substrate by using the solder, etc.
An optical switch module set forth in claim 25 of the present invention comprises a collimate portion for collimating individually a plurality of light signals respectively; a plurality of first optical deflecting elements for switching propagation directions of the light signals, which are passed through the collimate portion, individually respectively by utilizing an electrooptic effect; a common optical waveguide through which the light signals, which are passed through the plurality of first optical deflecting elements respectively, are propagated; a plurality of second optical deflecting elements for switching the propagation directions of the light signals, which are passed through the common optical waveguide, individually respectively by utilizing the electrooptic effect; a converging portion for converging the light signals, which are passed through the plurality of second optical deflecting elements, individually respectively; and a first substrate for supporting the collimate portion, the first optical deflecting elements, the common optical waveguide, the second optical deflecting elements, and the converging portion; wherein at least one of the first optical deflecting elements and the second optical deflecting elements is constructed by a second substrate, a first electrode formed on a first-substrate side surface of the second substrate, an optical waveguide formed on a first-substrate side surface of the first electrode and having an electrooptic effect, a wedge-shaped second electrode formed on a first-substrate side surface of the optical waveguide to oppose to the first electrode, and a leading electrode formed on the first-substrate side surface of the optical waveguide and connected electrically to the first electrode, whereby the second electrode and the leading electrode are jointed to electrodes of the first substrate.
The optical switch module of the present invention is constructed by jointing the second substrate on which the optical deflecting elements are formed to the first substrate on which the collimate portion, the common optical waveguide, and the converging portion are formed. As a result, the first substrate can be formed by the substrate having no electrooptic effect, so that the optical loss can be reduced rather than the case where the overall optical switch module is formed on the substrate having the electrooptic effect.